feat: Phase 1-3 优化全部完成

Phase 1 紧急修复（8项）:
- 社保城市选择改为可输入
- 社保上下限拆分（三险/医保独立基数）
- 公积金试算结果展示修复
- 花名册合同保存修复（日期ISO格式）
- 薪酬批次创建失败修复（城市过滤+错误处理）
- 证据链查看修复
- 个税计算修复（blank_employees读取基本工资）
- 加班费倍率读取配置

Phase 2 功能完善（3项）:
- 批量导入per-row异常捕获+导入按钮
- 单人发薪UI入口优化
- 解除协议模板补充（员工提出离职版）

Phase 3 后期规划（4项）:
- 工资表导入功能（POST /import/payroll + 前端入口）
- 大病险/长护险附加险种（extraInsurances JSON + 计算适配）
- 专项附加扣除按月录入（SpecialDeductionRecord模型 + 前端Tab）
- 预置河北省社保政策（seed数据）

backend/src/routes/payroll.routes.ts

@@ -41,10 +41,11 @@ router.get('/overtime', async (req: AuthRequest, res: Response, next: NextFuncti
 router.post('/overtime', async (req: AuthRequest, res: Response, next: NextFunction) => {
   try {
     const data = overtimeSchema.parse(req.body)
-    const hourlyWage = data.monthlyWage / 21.75 / 8
-    const weekdayPay = hourlyWage * 1.5 * data.weekdayHours
-    const weekendPay = hourlyWage * 2.0 * data.weekendHours
-    const holidayPay = hourlyWage * 3.0 * data.holidayHours
+    const otConfig = await prisma.overtimeConfig.findUnique({ where: { orgId: req.user!.orgId } }) ?? { weekdayRate: 1.5, weekendRate: 2.0, holidayRate: 3.0, monthlyDays: 21.75, dailyHours: 8 }
+    const hourlyWage = data.monthlyWage / otConfig.monthlyDays / otConfig.dailyHours
+    const weekdayPay = hourlyWage * otConfig.weekdayRate * data.weekdayHours
+    const weekendPay = hourlyWage * otConfig.weekendRate * data.weekendHours
+    const holidayPay = hourlyWage * otConfig.holidayRate * data.holidayHours
     const totalPay = weekdayPay + weekendPay + holidayPay
 
     const record = await prisma.overtimeRecord.upsert({
@@ -103,10 +104,11 @@ router.put('/overtime/:id', async (req: AuthRequest, res: Response, next: NextFu
     const weekendHours = data.weekendHours ?? existing.weekendHours
     const holidayHours = data.holidayHours ?? existing.holidayHours
 
-    const hourlyWage = monthlyWage / 21.75 / 8
-    const weekdayPay = hourlyWage * 1.5 * weekdayHours
-    const weekendPay = hourlyWage * 2.0 * weekendHours
-    const holidayPay = hourlyWage * 3.0 * holidayHours
+    const otConfig = await prisma.overtimeConfig.findUnique({ where: { orgId: req.user!.orgId } }) ?? { weekdayRate: 1.5, weekendRate: 2.0, holidayRate: 3.0, monthlyDays: 21.75, dailyHours: 8 }
+    const hourlyWage = monthlyWage / otConfig.monthlyDays / otConfig.dailyHours
+    const weekdayPay = hourlyWage * otConfig.weekdayRate * weekdayHours
+    const weekendPay = hourlyWage * otConfig.weekendRate * weekendHours
+    const holidayPay = hourlyWage * otConfig.holidayRate * holidayHours
     const totalPay = weekdayPay + weekendPay + holidayPay
 
     const record = await prisma.overtimeRecord.update({